The opioid crisis has hit Philadelphia particularly hard, with over 46 overdose deaths per 100,000 residents in 2017, twice the national average. In response, the City of Philadelphia developed an overarching prevention strategy, the Resilience Project, which includes both services targeted toward people who use opioids and neighborhood environment interventions that address the blighted conditions where most overdoses occur. The objective of this proposal, Studying the PhilAdelphia Resilience Project as a Response to Overdose (SPARROw), is to evaluate the effectiveness and implementation of two Resilience Project programs to reduce opioid overdose: (1) the Alternative Response Unit (ARU) that accompanies ambulances responding to overdoses and aims to deliver harm reduction and care linkage to people who refuse hospital transport, and (2) blight remediation of abandoned buildings and land. This application leverages a natural experiment within the Resilience Project implementation to evaluate its impact on overdose outcomes. We hypothesize that interventions targeted at the time and place of opioid overdose ? including the ARU and blight remediation ? will be more effective at preventing overdose compared to standard Emergency Medical Services (EMS) care or absence of environmental modifications. We will: 1) Determine the effectiveness of the Resilience Project ARU on opioid overdose outcomes for patients who refuse transport after overdose. Using a quasi-experimental design, we will compare the proximal overdose outcomes (rates and timing of treatment linkage) and distal overdose outcomes (fatal and non-fatal overdoses) for patients who receive ARU engagement compared to those who, due to timing or location restrictions, receive traditional EMS care alone. 2) Evaluate the impact of Resilience Project blight remediation activities on fatal and non-fatal opioid overdose. We will use a difference-in-difference design to compare fatal and non-fatal overdoses in the 60 days before and after any given remediation effort compared to the same time period in two nearby locations that did not get remediated but had comparable pre-blight remediation overdose rates. 3) Evaluate implementation of the Resilience Project by a) characterizing the fidelity of ARU intervention in Kensington, b) measuring factors that moderate ARU fidelity, including blight, c) assessing barriers and facilitators to ARU implementation, and d) determining the costs for ARU and blight remediation interventions. We will characterize which ARU components are completed for each patient encounter (take home naloxone, rapid treatment referral, transportation to treatment, obtain phone number, and/or phone follow-up). We will also measure potential moderating factors including ARU team composition and nearby blight in real time at ARU engagement locations using validated photographic methods. We will characterize barriers and facilitators to implementation with ARU provider interviews. Last, we will determine the costs for ARU and blight remediation to inform sustainability and dissemination efforts.